The invention relates generally to container inspection apparatus and deals more particularly with an apparatus for testing the sealability of the mouth of a container.
Two types of sealing surface defects are dips and saddles. A dip is a narrow depression in the bottle mouth and a saddle is a wide depression.
A wide variety of finish leak detectors were previously known such as those disclosed in U.S. Pat. Nos. 3,496,761 and 4,490,800. These detectors inspect the sealing surface of a bottle which is fed by a conveyor or auger screw to an inspection site located beneath the detector. The detector of U.S. Pat. No. 3,496,761 includes a test fitting which is lowered into engagement with the mouth of the bottle at the inspection site and forms an air-tight seal if the bottle mouth is properly formed--smooth, flat and generally horizontal; otherwise, a leak results. The sealability of the bottle mouth by the test fitting mimics the sealability of the bottle mouth by a cap or other type of commercial seal.
In various leak detectors previously known, air is injected into the bottle and pressure is sensed according to a variety of schemes. For example, in U.S. Pat. No. 3,496,761 a metered volume of air is injected into the container by a piston and cylinder assembly which forms a pump. At the conclusion of the discharge stroke of the piston and cylinder assembly, while the test fitting still closes the mouth of the container under test, the air pressure retained in the container is gauged to determine whether an excessive leakage takes place due to imperfections in the container mouth. While this system is effective in detecting flaws in the surface of a bottle mouth, it is limited in the rate at which it can inspect bottles. Moreover, this type of inspection system requires contact with the bottle and injection of air, and the fulfillment of each requirement may contaminate the bottle.
U.S. Pat. No. 3,555,980 to Mathias discloses another type of finish leak detection apparatus. The apparatus illuminates the rim of a bottle with a beam of radiant energy which is polarized so that it has an electric vector perpendicular to the top surface of the container. The container is rotated relative to the beam during inspection. Certain types of defects reflect a portion of the beam upwardly into a sensor which has its line of vision forming Brewster's angle with the direction of the beam. Because of the polarization and the angular relation, a defect makes a substantial reduction in the amount of radiant energy transmitted into the container.
U.S. Pat. No. 3,880,750 to Butler discloses another optical apparatus for inspecting the sealing surface of a glass container in which a light source focuses a thin line of light across the rim. A light sensor receives a deflection of this light from the rim to provide a reference level. A defect in the rim causes a rise or fall in the received light.
U.S. Pat. No. 4,026,414 to Ellinger discloses another optical apparatus for testing the sealing surface of a container in which a light sensing head made up of a mosaic of 30-40 light sensors in the form of a circular ring is supported above a bottle being inspected. A light source provides a beam through the central aperture which floods the mouth of the bottle and light is reflected upwardly from the bottle rim to the various sensors.
A general object of the present invention is to provide a detector to sense the sealability of a container mouth which detector is reliable and accurate and provides a high throughput.